The invention relates to an aircraft wing, especially a wing with a cross section which is suitable for high-speed flight and an angle of attack, the wing parts which influence the wing lift and which can be moved from an aerodynamically inactive servicing position to an aerodynamically efficient active position and from the active position back into the servicing position, being assigned to the wings.
According to Bernoulli's Law, gases which increase their flow velocity reduce their pressure. Winged aircraft use this physical principle. FIG. 1 shows in cross section a conventional wing 1 with a given angle of attack 2. The top 3 of the wing 1 is arched to the outside. The air flow 5 streaming over the wing 1 on the top 3 must traverse a greater (longer) path than on the bottom 4 of the wing 1. The underpressure (lift arrows 7 in FIG. 1) thus resulting on the top 3 of the wing 1 equalizes the weight of the aircraft in horizontal flight and keeps it in the air.
By changing the speed, by choosing the angle of attack 2 and/or the aerodynamically efficient surface of the wings, the behavior in flight can be influenced. The lift which is formed on the wing of an aircraft is directly proportional to the area exposed to the air flow and proportional to the square of the speed of the air flow streaming over this wing. Furthermore, the lift is roughly proportional to the angle of attack of the wing as long as it remains in the range of roughly +/−14 degrees. Larger angles lead to so-called “stalling”, i.e. to separation of the air stream over the wing.
Aircraft designers try to produce the best possible ratio of lift and drag. But since this ratio is dependent on various factors such as the weight of the aircraft or the speed of the air streaming over the aerodynamically efficient aircraft parts, the attempt is made to match the lift and drag of aircraft to the conditions or applications prevailing at the time. A transport aircraft designed for subsonic operation has a lift-drag ratio of roughly 20, a glider on the other hand has a ratio of 30 or more. In supersonic flight the attainable ratio of lift/drag drops to below 10.
Winged aircraft should be able to change their aerodynamic lift behavior to meet the aerodynamic and economic requirements of low-speed and high-speed flight, increased or reduced payload, optimization of range and fuel consumption and use of long or short runways.
In the prior art, measures have been proposed for changing the lift of aircraft wings and adapting to different situations. One proposal consists in using inflatable wings or wing parts.
Other proposals (DE 20 26 054 B) relate to movable parts within the wings which are designed to change their profile by arching the (flexible) outside skin of the wing. Both possibilities are suitable, if at all, only for light, slow-flying, winged aircraft. Another, still extraordinarily complex and therefore expensive possibility is tiltable wings.
FIG. 2 shows the currently most common measures for changing the lift of a wing, specifically using landing flaps (underwing flaps) 10. These landing flaps 10 develop their action by their lengthening the rear, often also the front part of the wing 1 to the bottom. In this way the lift-generating profile on the top 3 of the wing 1 is also lengthened. This increases the lift 7. But since on the bottom 4 of the wing 1 when the angle of attack 2 is not changed a cavity 12 is formed, strong turbulence 13 forms in flight and leads to the known “buffeting” of the aircraft with the flaps 10 extended, therefore for example in the landing approach.
These landing flaps 10 are conventionally integrated into the wings and are extended on them if necessary, but can also be accommodated as described in DE 23 53 245 C in one or more chambers in the fuselage of the aircraft and from there are moved into their operating position near the wing edges (front edge and rear edge) But since in this as in all other types of application of lift flaps which act on the front and/or rear edges of the wings the remaining wing profile and the angle of attack remain unchanged, narrow limits are imposed on this form of changing lift.
For technical reasons and for reasons of stability of the takeoff and landing configuration the surface enlargement cannot exceed a certain amount, the required wing cross section cannot fall below a certain amount and the angle of attack of the wing cannot be changed. The cross section and length of the wing must maintain a certain minimum. For reasons of efficiency, but at the cost of likewise desirable versatility with reference to their characteristics, therefore aircraft types which are matched to relatively narrow applications have been developed. Attempts to increase the versatility of possible applications with existing, possibilities (VTOL, STOL, tilt wing aircraft and convertiplanes) are less economical and also not satisfactory in the aerodynamic properties attainable to date because they are extremely expensive.
U.S. Pat. No. 4,890,803 A shows and describes an aircraft wing of the initially mentioned type which has on its top a step which extends essentially over its entire length. The height of this step on the top of the wing can be changed by swivelling a “flap” to change the aerodynamic properties of the wing. In the embodiment shown in FIG. 4 of U.S. Pat. No. 4,890,803 A the flap in the lengthwise direction of the aircraft wing can be adjusted to move it into a receiving space in the lower part of the fuselage of the aircraft or out of it again. Thus it will become possible, in addition to swivelling the flap around the axis which lies in the area of the rear edge of the wing, to also change its effective size (length) in order to change the lift force, therefore the aerodynamic properties of the wing.